monerod --test-drop-download vs --fast-block-sync

Question

As per the help command

--test-drop-download : For net tests: in download, discard ALL blocks instead checking/saving them (very fast)

--fast-block-sync arg (=1) : Sync up most of the way by using embedded, known block hashes.

What is the difference between these two modes of syncing?

Answer 1

The help strings pretty much describe the differences.

The --test-drop-download version wont save the blocks, it's used for testing downloading of blocks.

The --fast-block-sync is a mode for normal operation (not testing) which will still save the downloaded blocks.